Flow field vortices generated by fluid flow over aerodynamic surfaces can buffet and fatigue any downstream structure exposed to these vortices. Vortices can be generated at the fore body of an aircraft or other upstream structure, and damage control surfaces, engines, after body/empennage, nacelles, turrets, or other structures integrated into the airframe. Additionally, these vortices can be ingested within engine air intakes or other like air inlets leading to poor performance and/or stalling of the aircraft engines. Stalling the aircraft engine creates a potentially hazardous condition.
Next generation aircraft, such as blended wing body, compound this problem by incorporating gas turbine inlets with serpentine spines within the air frame. Additionally, exotic aperture shapes for the inlet and outlet may cause excessive propulsion performance losses. These losses emanate from strong secondary flow gradients in the near wall boundary of the airflow, which produce coherent large-scale vortices.
These vortices can not only cause damage to downstream components on an aircraft, but can seriously damage downstream aircraft as well. To avoid these hazardous inter-aircraft interactions, aircraft are normally separated in time and space to avoid wake turbulence and the buffeting effects of this turbulence on downstream aircraft. Sufficient separation in time and space for take-off, cruise, approach and landing help to ensure that an encounter with another craft's wake turbulence is unlikely or sufficiently weak to avoid causing harm.
In the past, adverse flow field vortices were avoided by redesigning the aircraft in order to remove components from the path of flow field vortices. Alternatively, the components in the path of the flow field vortices were structurally hardened or replaced more frequently to avoid failures resulting from these stresses. Placing components, such as engines or control surfaces, in non-optimal positions in order to reduce these stresses often results in reduced vehicle performance. Similarly, adding structural weight to support increased stress loads caused by the flow field vortices also results in reduced vehicle performance.
Another solution employs passive vortex generator veins to mitigate the effects of flow field vortices. However, these veins result in increased weight and reduced performance over the aircrafts entire operating envelope. Vortex generators are small wing like sections mounted on an aerodynamic surface exposed to the fluid flow and inclined at an angle to the fluid flow to shed the vortices. The height chosen for the best interaction between the boundary layer and the vortex generator is usually the boundary layer thickness. The principle of boundary layer control by vortex generation relies on induced mixing between the primary fluid flow and the secondary fluid flow. The mixing is promoted by vortices trailing longitudinally near the edge of the boundary layer. Fluid particles with high momentum in the stream direction are swept along helical paths toward the duct surface to mix with and, to some extent replace low momentum boundary layer flow. This is a continuous process that provides a source to counter the natural growth of the boundary layer creating adverse pressure gradients and low energy secondary flow accumulation.
The use of vortex generators to reduce distortion and improve total pressure recovery has been applied routinely. Many investigations have been made in which small-geometry surface configurations effect turbulent flow at the boundary layers. Particular attention has been paid to the provision of so-called riblet surfaces in which an array of small longitudinal rib-like elements known as riblets extend over the turbulent boundary layer region of a surface in the direction of fluid flow over the surface, to reduce momentum transport or drag. Experimental results indicate that net surface drag reductions of up to about 7% can be achieved. However, these structure used to induce vortices are fixed and provide no mechanism to actively manipulate the vortex generation needed to improve a dynamic flow condition.
As computers increasingly leaved fixed locations and are used in direct physical applications, new opportunities are perceived for applying these powerful computational devices to solve real world problems in real time. To exploit these opportunities, systems are needed which can sense and act. Micro-fabricated Electro-Mechanical Systems (MEMS) are perfectly suited to exploit and solve these real world problems.
MEMS offer the integration of micro-machined mechanical devices and microelectronics. Mechanical components in MEMS, like transistors in microelectronics, have dimensions that are measured in microns. These electro-mechanical devices may include discrete effectors and sensors.
Therefore, a need exists for a system and method to shed these flow field vortices to avoid intra-vehicular and inter-vehicular buffeting and fatigue. Furthermore, a need exists for a solution that does not require increased size and weight, or reduced performance.